sql server database design_问答_开发者_运维开发者技术经验分享

I am planning to create a website using ASP.NET and SQL Server. However, my plan for the database design leaves me wondering if there is a better way.

The website will serve as a repository of information for various users. I figure I would have two databases, a Membership and Profile database.

The profile database would contain user data for all users, where each user may hav开发者_运维技巧e ~20 tables. I would create the tables when the user account is created and generate a key used to name the tables. The tables are not directly related.

For Example a set of tables for two different users could look like:

User1 Tables - TransactionTable_Key1, AssetTable_Key1, ResearchTable_Key1 ....;
User2 Tables - TransactionTable_Key2, AssetTable_Key2, ResearchTable_Key2 ....;

The Key1, Key2 etc.. values would be retrieved based on the MembershipID data when the account was created. This could result in a very large number of tables over time. I'm not sure if this will limit scalability by setting up the database in this way. Any recommendations?

Edit: I should mention that some of these tables would contain 20k+ rows.

Realistically it sounds like you only really need one database for this.

From the way you worded your question, it sounds like you're trying to dynamically create tables for users as they create accounts. I wouldn't recommend this method.

What you want to do is create a master table that contains a primary key for each individual user. I'm assuming this is the Membership table. Then create the ~20 tables that you need for the profiles of these members. Every record, no matter the number of users that you have, will go into these tables. These 20 tables would need to have a foreign key pointing to the unique identifier of the Membership table.

When you want to query a Member for their user information, just select from the tables where the membership table's primary Id matches the foreign key in the profile tables.

This would result in only a few tables in the end and is easily maintainable and follows better database design.

Your ORM layer (EF, LINQ, DAL code) will hate having to deal with one set of tables per tenant. It is much better to have either one set of tables for all tenant in a single database, or a separate database per tenant. The later is only better if schema upgrade has to be vetted by tenant (like Salesforce.com has). If you can afford to upgrade all tenant to a new schema at once then there is no reason for database per tenant.

When you design a schema that hold multiple tenant the important things to remember are

don't use heaps, all tables must be clustered index
add the tenant ID as the leftmost key to every clustered
add the tenant ID as the leftmost key to every non-clustered index too
add the Left.tenantID = right.tenantID predicate to every join
add the table.TenantID = @currentTenantID to every query

These are fairly simple rules and if you obey them (with no exceptions) you will get a perfect partitioning per tenant of every query (no query will ever ever scan rows in a range of a different tenant) so you eliminate contention between tenants. To be more through, you can disable lock escalation to make sure no tenant escalates to block every other tenant.

This design also lends itself to table partitioning and to sharing the database for scale-out.

You definitely don't want to create a set of tables for each user, and you would want these only in one database. Even with SQL Server 2008's large capacity for tables (note really total objects in database), it would quickly become unmanageable. Your best bet is to use 20 tables, and separate them via a column into user areas. You might consider partitioning the tables by this user value, but that should be tested for performance reasons too.

Yes, since the tables only contain id, key, and value, why not make one single table?

Have the columns: id, user ID, key, value

Put an Index on the user ID field.

A key idea behind a relational database is that the table structure does not change. You create a solid set of tables, and these are the "bones" of your application.

Cheers, Daniel

Neal,

The solution really depends on your requirement. If security and data access are concern and you have only a handful of users, you can set up a different db for each user with access for him set to only his/her database.

Other wise, what Daniel Williams suggested is a good alternative where you have one DB and tables laid out with a indexed column partitioning the users data rows.

It's hard to tell from the summary, but it looks like you are designing for dynamic attribution by user. This design approach is called EAV (Entity-Attribute-Value) and consists of a simple base collection key (UserID, SiteID, ProductID...) and then rows consisting of name/value pairs. In a more complex version, categories are sometimes added as "super columns" to the tuple/row and provide sub-groupings for a set of name/value pairs.

Designing in this way moves responsibility for data type integrity, relational integrity and tuple integrity to the application layer.

The risk with doing this in a relational system involves the breaking of the tuple or row into a set of rows. Updates, deletes, missing values and the definition of a tuple are no longer easily accessible through human interaction. As your application evolves and the definition of a tuple changes, it becomes almost impossible to tell if a name/value pair is missing because it's part of an earlier-version tuple or because it was unintentionally deleted. Ad-hoc research as well becomes harder to manage as business analysts must keep an understanding of the virtual structure either in their heads or in documentation provided.

If you are looking to implement an EAV model, I would suggest you look at a non-relational solution (nosql) like MongoDB or CouchDB. These stores allow a developer to save and retrieve "documents" or json-formatted messages that are essentially made up of a collection of name/value pairs and can look very much like a serialized object. The advantage here is that you can store dynamic attribution without breaking your tuple. You always know that you have a complete tuple because you can store and retrieve it as a single "blob" of information that can be serialized and deserialized at-will. You can also update single attributes within the tuple, if that's a concern.

MongoDB also provides some database-like features such as multiple-attribute indexes, a query engine that is robust in comparison to other similar non-relational offerings and a sharding solution that is much less trouble than trying to do it with MySQL.

I hope this helps.